As one of the methods for making certain information contained in a memory medium obtainable, there is known the method of utilizing memorizable electroconductivity variation. According to this method, by effecting exposure corresponding to recording information on a specific photosensitive material, electroconductivity variation having memorizability is created at the exposed portion, and the recorded information can be visualized by, for example, various developing methods employed for electrostatic photography. Also, such photosensitive material which brings about memorizable electroconductivity variation by light may be considered for uses as an optical forming memorizable electroconductive circuit or an optical switching device, since the current flowing through the photosensitive material varies under the voltage applied state.
In the prior art, various memorizable photosensitive materials have been proposed for electrostatic photography (for example, U.S. Pat. Nos. 3,879,201 and 3,997,342).
However, in the memorizable photosensitive materials of the prior art, for obtaining a desired image, there are problems such as that the exposure dosage must be made relatively larger (10 mJ/cm.sup.2 to 100 mJ/cm.sup.2), and also that the time in which the memory effect is stably maintained is short (some 10 minutes to about 1 hour).
In view of the problems of the prior art, I have proposed various improvement techniques for the purpose of improving particularly exposure sensitivity (for example, Japanese Patent Application No. 167010/1977, Japanese Laid-Open Patent Publication No. 17358/1981, Japanese Patent Application No. 5233/1982). However, in this prior art, a sufficiently improved characteristic can be obtained with respect to exposure sensitivity, but there is the problem that memory stability is not yet sufficiently satisfactory.
On the other hand, various materials which undergo nonmemorizable electroconductivity variation have been known and utilized as optical switching devices or optical sensors. However, the converting devices of the prior art as mentioned above, while undergoing electroconductivity variation between ON-OFF changes in the relatively lower electroconductivity region, are not sufficiently satisfactory with respect to their switching sensitivity.